Transmitter, signal generation device, calibration method, and signal generation method

ABSTRACT

It is intended to provide a transmitter capable of correcting signal distortion with high accuracy. Provided are a test signal generator; a frequency characteristics corrector for correcting an amplitude characteristic and a phase characteristic of a test signal; a modulator; an envelope detector; a frequency characteristics calculator for calculating frequency characteristics of an envelope signal; and a coefficients calculator for calculating, on the basis of the frequency characteristics, correction coefficients to be used for correcting the amplitude characteristic and the phase characteristic of the test signal. The test signal generator generates a test signal in which signal loci in each of at least two pairs of quadrants of first to fourth quadrants of the IQ plane are not symmetrical with each other.

TECHNICAL FIELD

This disclosure relates to a transmitter, a signal generation device, acalibration method, and a signal generation method. For example, thedisclosure relates to calibration of frequency characteristics in atransmitter and an IQ signal calibration technique in a transmitter.

BACKGROUND ART

In wireless communication, distortion occurs depending on the frequencyof the signal when a baseband signal as a transmission signal isup-converted into a high-frequency signal and a high-frequency signal asa reception signal is down-converted into a baseband signal. Forexample, a frequency characteristics correcting device disclosed inPatent document 1 is known as a device for correcting signal distortion.

In the frequency characteristics correcting device of Patent document 1,in signal transmission by a transmission system circuit, part of atransmission signal is extracted by a coupling circuit and divided intoa low-frequency portion and a high-frequency portion by respective banddivision filters and outputs (power levels) of the respective filtersare detected by respective power detectors. Furthermore, in thefrequency characteristics correcting device, a variable equalizercircuit is controlled on the basis of a voltage that is obtained bycomparing outputs of the respective power detectors by a comparisoncircuit.

PRIOR ART DOCUMENTS Patent Documents

Patent document 1: JP-A-2001-16145

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In the frequency characteristics correcting device of Patent document 1,it is difficult to correct signal distortion with high accuracy.

This disclosure has been made in the above circumstances, and an objectof the present invention is to provide a transmitter, a signalgeneration device, a calibration method, and a signal generation methodwhich can correct signal distortion with high accuracy.

Means for Solving the Problems

This disclosure provides a transmitter comprising a test signalgenerator for generating a test signal; a frequency characteristicscorrector for correcting an amplitude characteristic and a phasecharacteristic of the test signal generated by the test signalgenerator; a modulator for modulating a corrected signal produced by thefrequency characteristics corrector through the correction; an envelopedetector for detecting an envelope of a modulated signal produced by themodulator through the modulation; a frequency characteristics calculatorfor calculating frequency characteristics of an envelope signal detectedby the envelope detector; and a coefficients calculator for calculating,on the basis of the frequency characteristics calculated by thefrequency characteristics calculator, correction coefficients to be usedby the frequency characteristics corrector to correct the amplitudecharacteristic and the phase characteristic of the test signal, whereinthe test signal generator generates a test signal in which signal lociin each of at least two pairs of quadrants of first to fourth quadrantsof the IQ plane are not symmetrical with each other.

Advantageous Effects of the Invention

The disclosure makes it possible to correct signal distortion with highaccuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example configuration of atransmitter according to a first embodiment of this disclosure.

FIGS. 2(A), 2(B), and 2(D) show example test signals generated by a testsignal generator used in the first embodiment of the disclosure, andFIG. 2(C) shows a phase characteristic of a test signal.

FIG. 3 shows an example relationship between components, havingrespective angular frequencies, of a test signal and their amplitudes inthe first embodiment of the disclosure.

FIG. 4 is a block diagram showing an example detailed configuration of afrequency characteristics corrector used in the first embodiment of thedisclosure.

FIG. 5 is a flowchart of a first example operation for calculatingcorrection coefficients in the transmitter according to the firstembodiment of the disclosure.

FIG. 6 is a flowchart of a second example operation for calculatingcorrection coefficients in the transmitter according to the firstembodiment of the disclosure.

FIG. 7 is a flowchart of a third example operation for calculatingcorrection coefficients in the transmitter according to the firstembodiment of the disclosure.

FIG. 8 shows a simulation result of an amplitude characteristic of atest signal in the first embodiment of the disclosure.

FIG. 9 shows a simulation result of an amplitude characteristic of thetest signal in the first embodiment of the disclosure.

FIG. 10 is a flowchart of a fourth example operation for calculatingcorrection coefficients in the transmitter according to the firstembodiment of the disclosure.

FIG. 11 is a graph showing an image of correction of the phasecharacteristic of a test signal into a linear phase characteristic inthe first embodiment of the disclosure.

FIG. 12 is a block diagram showing a modified configuration of thefrequency characteristics corrector used in the first embodiment of thedisclosure.

FIG. 13 is a block diagram showing an example configuration of a firstwireless apparatus according to the first embodiment of the disclosure.

FIG. 14 is a block diagram showing an example configuration of a secondwireless apparatus according to the first embodiment of the disclosure.

FIG. 15 is a block diagram of a transmitter according to a secondembodiment of the disclosure.

FIG. 16 is a block diagram showing an example detailed configuration ofan IQ imbalance corrector used in the second embodiment of thedisclosure.

FIG. 17 is a block diagram showing an example detailed configuration ofa modulator used in the second embodiment of the disclosure.

FIGS. 18(A) and 18(B) show examples of a first test signal and a secondtest signal in the IQ plane in the second embodiment of the disclosure.

FIG. 19 shows an example input/output characteristic of an envelopedetector used in the second embodiment of the disclosure.

FIG. 20 is a flowchart showing an example operation of a calculator usedin the second embodiment of the disclosure.

FIG. 21 is a table showing an example relationship between the detectedphase and the IQ imbalance direction in the second embodiment of thedisclosure.

FIG. 22 is a block diagram showing an example configuration of a firstwireless apparatus according to the second embodiment of the disclosure.

FIG. 23 is a block diagram showing an example configuration of a secondwireless apparatus according to the second embodiment of the disclosure.

MODE FOR CARRYING OUT THE INVENTION

Embodiments of this disclosure will be hereinafter described withreference to the drawings.

(Circumstances Leading to One Mode of Disclosure)

For example, signal distortion that depends on the frequency used tendsto appear in an analog circuit including a frequency converter whichperforms frequency conversion of a baseband signal and a high-frequencysignal, a power amplifier, and an LNA unit. In particular, in millimeterwave communication that handles frequencies in a wide band (e.g., 60 GHzband), the communication characteristics may be degraded to a largeextent because of a wide signal band.

When the frequency characteristics correcting device of Patent document1 is applied to millimeter wave communication, frequency characteristicsof signal distortion are corrected linearly on the basis of signaldetection results at several component frequencies. However, with thelinear correction, the communication characteristic may be degradedbecause it is insufficient for correction of large signal distortion asoccurs in the process of frequency conversion of a baseband signal or ahigh-frequency signal or amplification of a wideband high-frequencysignal. It is therefore necessary to correct signal distortion with evenhigher accuracy.

Transmitters, signal generation devices, and calibration methods whichcan correct signal distortion with high accuracy will be describedbelow.

Embodiment 1

FIG. 1 is a block diagram showing an example configuration of atransmitter 100 according to a first embodiment of the disclosure. Thetransmitter 100 is equipped with a test signal generator 101, a datagenerator 102, an MUX (multiplexer) 103, a frequency characteristicscorrector 104, a modulator 105, an envelope detector 106, a frequencycharacteristics calculator 107, a coefficients calculator 108, and amemory 109.

The test signal generator 101 generates a test signal for measurement ofdistortion produced by the transmitter 100, and outputs it to the MUX103. A test signal generation method will be described later in detail.

The data generator 102 generates a baseband signal containing data to betransmitted and outputs it to the MUX 103. For example, the data to betransmitted contains musical data or video data.

The MUX 103 selects the output of the test signal generator 101 or thatof the data generator 102, and outputs the selected signal to thefrequency characteristics corrector 104. More specifically, the MUX 103selects the output (test signal) of the test signal generator 101 in acalibration mode, and selects the output (baseband signal) of the datagenerator 102 in a data transmission mode. The MUX 103 also selects amode in which to specify an operation of the transmitter 100.

The frequency characteristics corrector 104 corrects the frequencycharacteristics of the output signal of the MUX 103 on the basis ofparameters (correction coefficients) stored in an LUT (lookup table)which is held by the memory 109, and outputs a resulting correctedsignal to the modulator 105. The frequency characteristics include anamplitude characteristic and a phase characteristic.

The modulator 105 modulates the corrected signal that is output from thefrequency characteristics corrector 104, and outputs a resultingmodulated signal (high-frequency signal). For example, the output V(t)of the modulator 105 is given by the following Equation (1):

[Formula 1]

V(t)=A(t)cos(ωt+θ(t))  (Formula 1)

The frequency of the output V(t) depends on ω in Equation (1) and isdetermined by f=ω/2π. The frequency is 60 GHz, for example.

The envelope detector 106 is equipped with an envelope detector 106A andan AD converter 1066 which is disposed downstream of the envelopedetector 106A so as to be connected to it in series.

The envelope detector 106A, which is formed by using a wave detectiondiode, detects an envelope of the high-frequency signal that is outputfrom the modulator 105. The envelope detector 106A receives part of theoutput energy of the high-frequency signal and detects the magnitude ofan envelope of the high-frequency signal.

A detected signal of the envelope detector 106A is given by thefollowing Formula (2):

[Formula 2]

c|A(t)| OR c|A(t)|²  (Formula 2)

Symbol c represents a constant.

The AD converter 106B converts the analog signal as the envelopedetection result into a digital signal, and outputs the digital signal(envelope signal) to the frequency characteristics calculator 107.

The frequency characteristics calculator 107 receives the signal(envelope signal) detected by the envelope detector 106, and calculatesfrequency characteristics of the envelope signal.

The coefficients calculator 108 calculates correction coefficients forcorrection of the frequency characteristics (amplitude characteristicand phase characteristic) of the test signal on the basis of thefrequency characteristics calculated by the frequency characteristicscalculator 107. The coefficients calculator 108 stores the calculatedcorrection coefficients in the LUT which is held by the memory 109.

The frequency characteristics calculator 107 and the coefficientscalculator 108 realize their functions by running programs that arestored in the memory 109. How the frequency characteristics calculator107 and the coefficients calculator 108 operate will be described laterin detail.

The transmitter 100 may be implemented by using a first integratedcircuit and a second integrated circuit. The first integrated circuitincludes the test signal generator 101, the data generator 102, the MUX103, the frequency characteristics corrector 104, the frequencycharacteristics calculator 107, the coefficients calculator 108, and thememory 109. The second integrated circuit includes the modulator 105 andthe envelope detector 106. Alternatively, all the constituent units ofthe transmitter 100 may be implemented as a single integrated circuit.

When the transmitter 100 is in the calibration mode, a detection systemincluding the envelope detector 106, frequency characteristicscalculator 107, and the coefficients calculator 108 operates.

Next, the test signal generator 101 will be described.

For example, the test signal generator 101 generates a test signal Sthat is represents by the following Equations (3):

$\begin{matrix}\left\lbrack {{Formulae}\mspace{14mu} 3} \right\rbrack & \; \\\left( \begin{matrix}{I = {{K\; {\cos \left( {\omega_{m,n}t} \right)}} + d}} \\{Q = {K\; {\sin \left( {\omega_{m,n}t} \right)}}}\end{matrix} \right. & \left( {{Formula}\mspace{14mu} 3} \right)\end{matrix}$

In Equations (3), ω_(m, n) is the angular frequency, d is a constantindicating an offset amount, and K is a constant representing theamplitude.

The frequency of the test signal S which is generated by the test signalgenerator 101 depends on ω_(m, n)t in Equation (3) and is determined byf=ω_(m, n)t/2π. For example, the frequency of the test signal S is 100MHz or 500 MHz. That is, the angular frequency ω_(m, n) in Equation (3)is sufficiently lower than the angular frequency ω in Equation (1).

FIG. 2(A) is a diagram in which the test signal S of Equation (3) isshown in the IQ plane. The test signal S is represented by a circle thatis offset by the distance d from a circle C whose center is located atthe origin O of the IQ plane and that is the same in amplitude as thetest signal S. The test signal S may rotate at a constant speed alongthe circle but need not always do so.

The test signal generator 101 may generate, as a test signal, an IQsignal that is not given by Equations (3). The test signal generator 101may generate an IQ signal that is symmetrical with respect to the I axis(see FIG. 2(B)) or the Q axis.

The test signal generator 101 may generate an IQ signal that is obtainedby rotating an IQ signal that is symmetrical with respect to the I axisor the Q axis about the origin O of the IQ plane. Also in these cases,the center of the test signal S is offset by a prescribed amount fromthe origin O. The test signal S may rotate at a constant speed along theline but need not always do so. The I axis and the Q axis are examplesof a reference axis.

Where the test signal shown in FIG. 2(A) or 2(B) is generated by thetest signal generator 101, it has such a characteristic that as shown inFIG. 2(C) its amplitude varies monotonously as its phase varies from φto φ+180°, φ being a phase of its line of symmetry (the reference axispassing through the origin). The case of FIG. 2(D) is different fromthat of FIG. 2(B) in that the line of symmetry has a phase φ.

That is, it suffices that the loci of the test signal in each of atleast two pairs of quadrants of the first to fourth quadrants of the IQplane be not symmetrical with each other.

For example, in the case of FIG. 2(A), the loci in the first and secondquadrants is not symmetrical with each other, the loci in the first andthird quadrants is not symmetrical with each other, the loci in thesecond and fourth quadrants is not symmetrical with each other, the lociin the first and fourth quadrants is symmetrical with each other, andthe loci in the second and third quadrants is symmetrical with eachother.

In the case of FIG. 2(B), the loci in the first and second quadrants isnot symmetrical with each other, the loci in the first and thirdquadrants is not symmetrical with each other, the loci in the second andfourth quadrants is not symmetrical with each other, the loci in thefirst and fourth quadrants is symmetrical with each other, and the lociin the second and third quadrants is symmetrical with each other.

In the case of FIG. 2(D), the loci in every pair of quadrants are notsymmetrical with each other.

Where the test signal C shown in FIG. 2(A) with which the circle havingthe center at the origin is drawn in the IQ plane is used, the magnitudeof an envelope detected by the envelope detector 106 is constant.Therefore, this test signal C does not have an AC signal component andhence it is difficult to obtain its phase characteristic.

The magnitude of an envelope can be varied when the test signalgenerator 101 generates a test signal S that is offset from the originby a prescribed amount. Therefore, an amplitude characteristic and aphase characteristic can be acquired by using such a test signal S.

As shown in FIG. 3, the test signal generator 101 sweeps the angularfrequency ω_(m, n) of the test signal S in order from n=1 to N. FIG. 3shows an example relationship between components, having the angularfrequencies ω_(m, n), of the test signal S and their amplitudes. In FIG.3, the sweep range of the frequency (=ω_(m)/2π) of the test signal S is−1 GHz to 1 GHz, for example, and the interval between adjoiningcomponent frequencies is 100 MHz, for example.

For example, a test signal having an angular frequency ω_(m, 1) is usedas a first test signal S₁ and a test signal having an angular frequencyω_(m, n) is used as an nth test signal S_(n). Finally, a test signalhaving an angular frequency ω_(m, N) is used as an Nth test signalS_(N). The test signal S_(n) is a component, having the angularfrequency ω_(m, n), of the test signal S.

The value N is the number of samples for determining frequencycharacteristics of the test signal S_(n). It is preferable that the testsignal generator 101 set the value N taking into consideration at whatfrequency interval frequency characteristics are to be analyzed and atwhat resolution frequency characteristics are to be corrected. The valueN may be set in advance.

Next, the frequency characteristics corrector 104 will be described.

FIG. 4 is a block diagram showing an example detailed configuration ofthe frequency characteristics corrector 104.

The frequency characteristics corrector 104 is equipped with a Fouriertransformer 204, a multiplier 205, and an inverse Fourier transformer206.

The Fourier transformer 204 converts a time-domain signal which is anoutput signal of the MUX 103 into a frequency-domain signal. Since theoutput signal of the MUX 103 is an IQ signal, the Fourier transformer204 converts it as complex data. The Fourier transformer 204 performsfast Fourier transform (FFT), for example.

The multiplier 205 multiples the frequency-domain signal that is outputfrom the Fourier transformer 204 by correction coefficients that arestored in the LUT held by the memory 109.

The inverse Fourier transformer 206 converts the frequency-domain signalthat is output from the multiplier 205 into a time-domain signal. Theinverse Fourier transformer 206 performs inverse fast Fourier transform(IFFT), for example.

Next, a description will be made of an example operation for calculatingcorrection coefficients for correction of frequency characteristics onthe basis of a test signal in the transmitter 100.

FIG. 5 is a flowchart of a first example operation for calculatingcorrection coefficients for correction of frequency characteristics onthe basis of a test signal S in the transmitter 100. The example of FIG.5 assumes that coefficients z_(n) of the respective angularfrequenciesω_(m, n) are calculated by one frequency sweep. In theexample of FIG. 5, the coefficients z_(n) are correction coefficients.

First, the test signal generator 101 sets variable n to an initial value“1” (step S401).

The test signal generator 101 then generates a test signal S and setsits angular frequency to the angular frequency ω_(m, n) (step S402).

During a period when the test signal generator 101 is performing afrequency sweep, the frequency characteristics corrector 104 does notperform frequency characteristics correction or performs frequencycharacteristics correction by setting the coefficients z_(n) stored inthe LUT to “1.”

Then the frequency characteristics calculator 107 receives an envelopesignal corresponding to a test signal S_(n) having the angular frequency(ω_(m, n) and Fourier-transforms it (step S403). That is, the frequencycharacteristics calculator 107 has a Fourier transformer. To increasethe calculation efficiency, the frequency characteristics calculator 107uses fast Fourier transform (FFT), for example.

The frequency characteristics calculator 107 then extracts componentcomplex data a_(n)+jb_(n) of the angular frequency ω_(m, n) in the IQplane (step S404).

The frequency characteristics calculator 107 may calculate an amplitudem_(n) and a phase θ_(n) according to respective Equations (4) and (5) onthe basis of the extracted data a_(n)+jb_(n):

[Formula 4]

m _(n)=√{square root over (a _(n) ² +b _(n) ²)}  (Formula 4)

[Formula 5]

θ_(n)arg(a _(n) +jb _(n))  (Formula 5)

That is, frequency characteristics, including an amplitudecharacteristic and a phase characteristic, of the component of theangular frequency ω_(m, n) are obtained by executing step S404. Thefrequency characteristics are of the transmitter 100 itself and, morespecifically, are frequency characteristics of distortion thatoriginates from, for example, the analog circuit of the transmitter 100.

Subsequently, the coefficients calculator 108 calculates a coefficientz_(n) which is complex data for correction of the frequencycharacteristics of the transmitter 100, and has the information of thecoefficient z_(n) held inside the coefficients calculator 108temporarily (step S405). The coefficient 4 is given by the followingEquation (6):

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 6} \right\rbrack & \; \\{z_{n} = \frac{1}{a_{n} + {j\; b_{n}}}} & \left( {{Formula}\mspace{14mu} 6} \right)\end{matrix}$

The coefficient z_(n) is also given by the following Equation (7) usingthe amplitude m_(n) and the phase θ_(n):

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack & \; \\{z_{n} = {\frac{1}{m_{n}}^{{- j}\; \theta_{n}}}} & \left( {{Formula}\mspace{14mu} 7} \right)\end{matrix}$

That is, the coefficients calculator 108 calculates a coefficient z_(n)which is the reciprocal of the complex data a_(n)+jb_(n) of the angularfrequency ω_(m, n) of the test signal S. The coefficient z_(n) is aninverse characteristic of the frequency characteristic of thetransmitter 100.

Then the test signal generator 101 judges whether or not the sweep hasreached the test signal S_(N) which is the last angular frequencycomponent (step S406). That is, the test signal generator 101 judgeswhether n≧N is satisfied or not.

If the sweep has not reached the last test signal S_(N) yet, for afrequency analysis using the next test signal, the test signal generator101 changes the angular frequency ω_(m, n) of the test signal S_(n)(step S407). That is, “1” is added to variable n. The process thenreturns to step S402.

On the other hand, if the sweep has reached the last test signal S_(N),the coefficients calculator 108 stores, in the LUT held by the memory109, the information of coefficients z_(n) of the respective angularfrequencies ω_(m, 1) to ω_(m, N) which are held therein temporarily(step S408).

According to the process of FIG. 5, frequency component of test signalsS_(n) of the respective angular frequencies ω_(m, n) are analyzed andcoefficients z_(n) are calculated, whereby the frequency characteristicscan be corrected in such a manner that an amplitude characteristic and aphase characteristic of the test signals S_(n) are taken intoconsideration. Since a modulated signal is generated from a correctedbaseband signal, a signal having a flat amplitude characteristic andphase characteristic can be transmitted. Furthermore, since an inversecharacteristic can be calculated easily because the reciprocal of afrequency characteristic of the transmitter 100 is used.

In the process of FIG. 5, as for the timing of writing of coefficientsto the LUT, coefficients z_(n) of all the angular frequencies ω_(m, 1)to ω_(m, n) are calculated and then stored in the memory 109. That is,the coefficients calculator 108 stores calculated coefficients z_(n) inthe LUT after a sweep of the N angular frequencies ω_(m, n) of the testsignals S_(n). Alternatively, the coefficients calculator 108 may storea coefficient z_(n) of each angular frequency ω_(m, n) in the memory 109every time it is calculated.

FIG. 6 is a flowchart of a second example operation for calculatingcorrection coefficients for correction of frequency characteristics onthe basis of a test signal S in the transmitter 100. In the example ofFIG. 6, while coefficients z_(n) of the respective angular frequenciesω_(m, n) are calculated repeatedly, coefficients y_(n) which are basedon the coefficients z_(n) are stored in the LUT. The coefficients z_(n)are updated successively.

In FIG. 6, the coefficients z_(n) are coefficients indicating residualerrors of correction and are coefficients for calculation ofcoefficients y_(n). The coefficients yn are correction coefficients. Acoefficient w is a weighting coefficient in adding residual errors z_(n)and is selected from a range of 0 to 1. For example, the coefficient wis set at 0.5.

First, the test signal generator 101 sets variable n to an initial value“1” and sets variables y_(n) to initial values “0” (step S501).

Then the transmitter 100 executes the same steps S402-S406 as shown inFIG. 5. When one-round frequency characteristic analyses to the lasttest signal S_(N) have been completed and coefficients z_(n) have beencalculated, the process moves to step S502.

The coefficients calculator 108 adds the calculated coefficients z_(n)to the respective coefficients y_(n) while giving the weight w to theformer (step S502). More specifically, the coefficients calculator 108calculates y_(n)=y_(n)+w×z_(n).

Subsequently, the coefficients calculator 108 stores the information ofthe calculated coefficients y_(n) in the LUT which is held by the memory109. If the LUT is already stored with information of coefficientsy_(n), it is updated by the new information.

The coefficients calculator 108 then calculates differences between thecurrent coefficients y_(n) with the coefficients y_(n) calculated lasttime. The process is finished if the differences are smaller than orequal to a predetermined threshold value. The process returns to stepS402 if the differences are larger than the predetermined thresholdvalue (step S504).

In the process of FIG. 6, the coefficients calculator 108 updates thecoefficients y_(n) stored in the LUT while calculating coefficientsy_(n) as correction coefficients repeatedly. For example, thecoefficients y_(n) are updated by a result of adding weightedcoefficients z_(n) to them.

With the process of FIG. 6, the correction accuracy of the coefficientsy_(n) as correction coefficients is increased because coefficients z_(n)of the respective angular frequency ω_(m, n) are calculated repeatedly.Since coefficients z_(n) are calculated repeatedly and coefficientsy_(n) are calculated using the coefficient w, residual errors comecloser to zero gradually and the correction accuracy is increasedfurther.

Since a modulated signal is generated from a corrected baseband signal,a signal having a flat amplitude characteristic and phase characteristiccan be transmitted.

FIG. 7 is a flowchart of a third example operation for calculatingcorrection coefficients for correction of frequency characteristics onthe basis of a test signal S in the transmitter 100. Differences fromthe process of FIG. 6 will be described. In FIG. 7, coefficients z_(n)of the respective angular frequency ω_(m, n) are calculated repeatedly Rtimes.

First, at step S505, the test signal generator 101 sets variable n to aninitial value “1,” sets variables y_(n) to initial values “0,” and setsvariable r to an initial value “1.”

At step S506, the coefficients calculator 108 judges whether or notcoefficients y_(n) have been calculated a prescribed number of times (Rtimes). More specifically, the coefficients calculator 108 judgeswhether r≧R is satisfied or not.

If it is judged that coefficients y_(n) have not been calculated R timesyet, at step S507 the coefficients calculator 108 adds “1” to variable rand initializes variable n to “1.” On the other hand, if it is judgedthat coefficients y_(n) have been calculated R times, the transmitter100 finishes the process of FIG. 7.

Next, a description will be made of a simulation of correction offrequency characteristics.

FIG. 8 shows a simulation result of an amplitude characteristic of atest signal. FIG. 9 shows a simulation result of a phase characteristicof the test signal. FIGS. 8 and 9 show results of a simulation performedaccording to the operation of FIG. 5, 6, or 7.

In the simulation, in generating a test signal, the test signalgenerator 101 sets the sampling frequency to 3.52 GHz and sets thecoefficients K and d used in Equations (3) to 1 and 0.1, respectively.The test signal generator 101 sweeps f_(m) (=2πω_(m)) in a range of −1.1to +1.1 GHz at intervals of 100 MHz.

A second-order Butterworth filter in which the cutoff frequency is 300MHz and the pass frequency is shifted to the negative direction by 352MHz is assumed as a filter that simulates the frequency characteristicsof the transmitter 100.

In FIGS. 8 and 9, the solid line L1 represents a characteristic of thefilter and white circles D1 represent a frequency characteristic(detected characteristic) of the test signal measured by the frequencycharacteristics calculator 107. It is seen from FIGS. 8 and 9 that thefilter characteristic and the detected characteristic coincide with eachother. Therefore, it is confirmed that an amplitude characteristic and aphase characteristic can be detected accurately by the detection systemof the transmitter 100.

In FIGS. 8 and 9, the broken line L2 represents a frequencycharacteristic (corrected characteristic) of a signal as corrected bythe frequency characteristics corrector 104 after calculation ofcorrection coefficients. The broken line L2 representing a phasecharacteristic coincides with the line of “0.” That is, when a signal iscorrected by the frequency characteristics corrector 104 usingcorrection coefficients which represent an inverse characteristic and aresulting corrected signal is modulated, a signal to be transmittedcomes to have a flat phase characteristic and amplitude characteristic.

Furthermore, frequency characteristics can be analyzed properly even fora filter characteristic that is offset from the center of a measurementfrequency range and is not symmetrical.

Next, a description will be made of a case that the frequencycharacteristics of the transmitter 100 are corrected so as to have alinear phase characteristic.

FIG. 10 is a flowchart is a flowchart of a fourth example operation forcalculating correction coefficients for correction of frequencycharacteristics on the basis of a test signal S in the transmitter 100.In FIG. 10, coefficients x_(n) are correction coefficients. In theexample of FIG. 10, correction is made so as to attain a linear phasecharacteristic instead of making correction until a signal that isoutput from the transmitter 100 exhibits a flat phase characteristic(equivalent to the characteristic represented by the broken line L2 inFIG. 9).

First, the same steps S401-S403 as shown in FIG. 5 are executed. Theprocess moves to step S601 upon completion of Fourier transform on atest signal of an angular frequency ω_(m, n).

The frequency characteristics calculator 107 extracts component complexdata a_(n)+jb_(n) of the angular frequency ω_(m, n) the IQ plane. Thefrequency characteristics calculator 107 calculates an amplitude m_(n)and a phase θ_(n) from the extracted data a_(n)+jb_(n) according toEquations (4) and (5), respectively (step S601).

Then the coefficients calculator 108 calculates a difference Δθ_(n)between the phase θ_(n) and a linear phase characteristic θ_(i, n), thatis, calculates Δθ_(n)=θ_(n)−θ_(i, n). The linear phase characteristicθ_(i, n) is a characteristic that the phase decreases linearly as thefrequency increases (see FIG. 11). The information of the linear phasecharacteristic θ_(1, n) is held by the memory 109 in advance.

The coefficients calculator 108 then calculates a coefficient x_(n)which is complex data for correction of the frequency characteristics ofthe transmitter 100, and has the information of the coefficient x_(n)held inside the coefficients calculator 108 temporarily (step S405). Thecoefficient x_(n) is given by the following Equation (8) using theamplitude m_(n) and the phase difference Δθ_(n):

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 8} \right\rbrack & \; \\{x_{n} = {\frac{1}{m_{n}}^{{- {j\Delta}}\; \theta_{n}}}} & \left( {{Formula}\mspace{14mu} 8} \right)\end{matrix}$

That is, the coefficients calculator 108 calculates a coefficient x_(n)as a correction coefficient on the basis of the amplitude m_(n) and thedifference between the phase θ_(n) of the component complex data and thelinear phase characteristic θ_(i, n) of the angular frequency ω_(m, n)of the test signal S and the linear phase characteristic θ_(i, n).

In the transmitter 100, the phase of the test signal delays more as thefrequency increases (see FIG. 9) because its transmission system usuallyhas a positive delay time. The transmission system includes the testsignal generator 101, the data generator 102, the MUX 103, the frequencycharacteristics corrector 104, and the modulator 105.

The process of FIG. 10 can produce such coefficients x_(n) that thephase characteristic is made close to a linear phase characteristictaking a certain degree of phase delay into consideration instead ofproducing a characteristic that is completely inverse in phase to thefrequency characteristics of the transmitter 100. Therefore, thetransmitter 100 can produce a satisfactory amplitude characteristic andphase characteristic without the need for preparing a filter having anegative delay time.

Since it suffices to correct the phase characteristic of an outputsignal of the transmitter 100 into a linear phase characteristic, theamount of calculation can be made smaller than in the case of generatingcorrection amounts of an inverse characteristic, which enables effectiveuse of a time resource and a bit width resource. Therefore, even in thecase where a frequency characteristic having steep variations atparticular frequencies as in quantization noise is included, thecorrection accuracy can be increased by making correction into a linearphase characteristic by using one parameter (Δθ_(n)).

FIG. 11 is a graph showing an image of correction of the phasecharacteristic of a test signal into a linear phase characteristic.

In FIG. 11, the solid line L1 represents a filter characteristic of afilter that simulates the frequency characteristics of the transmitter100. White dots D1 represent a detected characteristic. The broken lineL2 represents a linear phase characteristic, that is, a correctedcharacteristic as corrected using coefficients x_(n) calculated atprescribed frequencies by the process of FIG. 10.

Next, a modification of the frequency characteristics corrector 104 willbe described.

FIG. 12 is a block diagram showing a modified configuration of thefrequency characteristics corrector 104.

In FIG. 12, the frequency characteristics corrector 104 is equipped witha digital filter 301. Where the digital filter 301 is used, coefficientsof the digital filter 301 are stored in the LUT. For example,coefficients of the digital filter 301 may be calculated byinverse-Fourier-transforming coefficients z_(n) (correctioncoefficients) in the coefficients calculator 108.

Where the digital filter 301 is provided, the configuration can besimplified because it is not necessary that the frequencycharacteristics corrector 104 be provided with a Fourier transformer andan inverse Fourier transformer.

Next, a description will be made of how the transmitter 100 operatesafter completion of the calibration.

After completion of the calibration, the transmitter 100 finishes thecalibration mode. Upon the finish of the calibration mode, thetransmitter 100 switches to the data transmission mode. Morespecifically, the MUX 103 shown in FIG. 1 selects the output of the datagenerator 102.

Then the frequency characteristics corrector 104 corrects an IQ signalthat is output from the data generator 102 by referring to the LUT inwhich the correction coefficients calculated by the coefficientscalculator 108 are stored. Subsequently, the modulator 105 modulates acorrected signal and a modulated signal is transmitted.

The transmitter 100 can correct the amplitude characteristic and thephase characteristic of a signal with high accuracy and hence can reducedistortion of a transmission signal. For example, the correction of thefrequency characteristics of the transmitter 100 is performed at thetime of power-on of the transmitter 100 or its reactivation from a sleepmode or before the start of a data transmission.

As seen from the above description, the transmitter 100 can correct,with high accuracy, frequency characteristics caused by frequencyconversion between a baseband signal and a high-frequency signal in, forexample, wireless communications in a wide frequency band. Furthermore,a transmitter can be realized in which an amplitude characteristic, aphase characteristic, and frequency characteristics are compensated soas to become flat in wireless communications in a wide frequency band.

Next, a wireless apparatus 400 including the transmitter 100 will bedescribed.

FIG. 13 is a block diagram showing an example configuration of thewireless apparatus 400. The wireless apparatus 400 is equipped with thetransmitter 100, a receiver 402, a duplexer 403, and an antenna 404.

The transmitter 100 corrects frequency characteristics, modulatesdesired data, and transmits a modulated signal. The receiver 402receives data from another communication apparatus. The duplexer 403separates a transmission signal and a reception signal from each other,whereby the antenna 404 is shared by transmission and reception.

The wireless apparatus 400 makes it possible to transmit data havingonly a low degree of distortion.

FIG. 14 shows another wireless apparatus 500 which is equipped with atransmission antenna 503 and a reception antenna 504 which are separatefrom each other.

(Circumstances Leading to Another Mode of Disclosure)

For example, conventional transmitters modulate a transmission signalusing an I signal and a Q signal (also called an IQ signal) and output amodulated signal. Where the same digital values are set for an I signaland a Q signal, the modulation accuracy should be high if the I signaland the Q signal have a phase different of 90° and the same amplitude.However, in practice, since transmitters include an analog circuit, an Isignal and a Q signal are different from each other in amplitude andtheir phase difference may deviate from 90°. Transmitters calibrate anIQ signal in the digital domain to make it closer to a desired state.

There is a conventional transmitter described below. This transmitteruses a sinusoidal single-sideband signal as a test signal. Anenvelope-detected signal is subjected to a frequency analysis and aphase of a frequency-analyzed signal is determined. The transmitterdetermines directivity of a gain error and a phase error from thethus-determined phase and performs calibration (refer to Referentialpatent document, for example).

Referential patent document: U.S. Pat. No. 7,881,402

An envelope detector which detects an envelope of a signal is used forcalibrating an IQ signal. The envelope detector is formed using a wavedetection diode, for example. In transmitters, an AD (analog-to-digital)converter which receives an output of the envelope detector is disposeddownstream of the envelope detector.

In conventional transmitters, to increase the accuracy of IQ signalcalibration, it is desirable to determine a reference phase. However, itis unclear how to determine a reference phase. For example, an exampletest signal for determining a reference phase of 0° is a test signal(I=cos ω_(m)t, Q=0) in which the gain error is made extremely large.Since the test signal has a wide dynamic range, the detection system isrequired to have a wide dynamic range. That is, the wave detection diodeis required to have a wide detection range or the AD converter isrequired to have a large number of bits.

In handling a signal in a relatively narrow frequency band (e.g., 1 GHzband), the modulation frequency of the AD converter can be set low andthe number of bits that can be handled by the AD converter (dynamicrange, vertical resolution) can be increased. In the AD converter, thenumber of bits that can be handled can be increased as the frequencyband becomes narrower because a tradeoff relationship exists between thefrequency band of an input signal and the number of bits. Therefore, itis highly probable that a signal in a relatively narrow frequency bandcan be detected correctly.

On the other hand, in handling a signal in a relatively wide frequencyband (e.g., 60 GHz band), it is necessary to set the modulationfrequency of the AD converter high and hence the number of bits that canbe handled by the AD converter becomes small. Therefore, for a testsignal having a wide dynamic range, it is difficult to determine anaccurate reference phase because of lowered detection accuracy and theaccuracy of the IQ calibration becomes insufficient.

A transmitter, a signal generation device, and a signal generationmethod which can increase the IQ calibration accuracy will behereinafter described.

Embodiment 2

FIG. 15 is a block diagram showing an example configuration of atransmitter 1100 according to a second embodiment of the disclosure. Thetransmitter 1100 is equipped with a test signal generator 1101, abaseband signal generator 1102, an MUX (multiplexer) 1103, an IQimbalance corrector 1104, a modulator 1105, an envelope detector 1106, acalculator 1107, and a memory 1108.

The test signal generator 1101 generates a test signal for measurementof IQ imbalance and outputs it to the MUX 103. The test signal generator1101 generates a test signal according to a detectable range of theenvelope detector 1106. A test signal generation method will bedescribed later in detail.

The baseband signal generator 1102 generates a baseband signal to beused for a communication and outputs it to the MUX 1103.

The MUX 1103 selects the test signal or the baseband signal, and outputsthe selected signal to the IQ imbalance corrector. The MUX 1103 selectsthe output of the test signal generator 1101 in a calibration mode(i.e., in calibrating the IQ signal), and selects the output of thebaseband signal generator 1102 in a data transmission mode (i.e., intransmitting the baseband signal).

The IQ imbalance corrector 1104 corrects the received IQ signal on thebasis of parameters (correction coefficients) stored in an LUT (lookuptable) which is held by the memory 1108, and outputs a resultingcorrected signal to the modulator 1105. IQ imbalance is corrected in thecorrection performed by the IQ imbalance corrector 1104. The IQimbalance includes an amplitude error and a phase error.

The modulator 1105 modulates the corrected signal that is output fromthe IQ imbalance corrector 1104, and outputs a resulting modulatedsignal (high-frequency signal).

The envelope detector 1106 includes an envelope detector 1106A and an ADconverter 11068 which is disposed downstream of the envelope detector soas to be connected to it in series. The envelope detector 1106A, whichis formed by using a wave detection diode, detects an envelope of thehigh-frequency signal that is output from the modulator 1105. The ADconverter 1106B converts the analog signal as the envelope detectionresult into a digital signal, and outputs the digital signal (envelopesignal) to the calculator 1107.

The calculator 1107 detects IQ imbalance by analyzing the envelopesignal. And the calculator 1107 calculates correction coefficients forcorrection of the IQ imbalance and updates the LUT which is held by thememory 1108. That is, the calculator 1107 has a function of a correctioncoefficients processor for calculating correction coefficients on thebasis of the envelope detected by the envelope detector 1106.

The calculator 1107 realizes its functions by running programs that arestored in a memory (not shown). How the calculator 1107 operates will bedescribed later in detail.

The memory 1108 has the LUT and stores various data and parameters. Thevarious parameters include a matrix c which includes correctioncoefficients.

The test signal generator 1101, the baseband signal generator 1102, theMUX 1103, the IQ imbalance corrector 1104, the calculator 1107, and thememory 1108 may be implemented as a first integrated circuit, and themodulator 1105 and the envelope detector 1106 may be implemented as asecond integrated circuit. Alternatively, all the constituent units ofthe transmitter 1100 may be implemented as a single integrated circuit.

Next, the IQ imbalance corrector 1104 will be described.

For example, the matrix c which is used for the IQ imbalance correctionis given by the following Equation (9) which uses values g_(c) andθ_(c). The value g_(c) is a value to contribute to correction of anamplitude error g_(e), and the value θ_(c) is a value to contribute tocorrection of a phase error θ_(e).

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 9} \right\rbrack & \; \\{c = \begin{pmatrix}\frac{\cos \; \frac{\theta_{c}}{2}}{\left( {1 - g_{c}} \right)\cos \; \theta_{c}} & \frac{{- \sin}\; \frac{\theta_{c}}{2}}{\left( {1 - g_{c}} \right)\cos \; \theta_{c}} \\\frac{{- \sin}\; \frac{\theta_{c}}{2}}{\left( {1 + g_{c}} \right)\cos \; \theta_{c}} & \frac{\cos \; \frac{\theta_{c}}{2}}{\left( {1 + g_{c}} \right)\cos \; \theta_{c}}\end{pmatrix}} & \left( {{Formula}\mspace{14mu} 9} \right)\end{matrix}$

When the amplitude error g_(e) and the phase error θ_(e) aresufficiently small, the values g_(c) and θ_(c) also become small and thematrix c can be approximated by the following Equation (10):

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 10} \right\rbrack & \; \\{c = \begin{pmatrix}{1 + g_{c}} & {{- \left( {1 + g_{c}} \right)}\frac{\theta_{c}}{2}} \\{{- \left( {1 - g_{c}} \right)}\frac{\theta_{c}}{2}} & {- \left( {1 - g_{c}} \right)}\end{pmatrix}} & \left( {{Formula}\mspace{14mu} 10} \right)\end{matrix}$

FIG. 16 is a block diagram showing an example detailed configuration ofthe IQ imbalance corrector 1104.

For example, the IQ imbalance corrector 1104 includes multipliers 1201,1202, 1203, and 1204 and adders 1205 and 1206.

The multiplier 1201 receives an I signal (pre-correction I signal) thatis output from the MUX 1103 and a correction coefficient c(1, 1) that isstored in the LUT, and multiplies them together. The multiplier 1202receives the I signal (pre-correction I signal) that is output from theMUX 1103 and a correction coefficient c(2, 1) that is stored in the LUT,and multiplies them together. The multiplier 1203 receives a Q signal(pre-correction Q signal) that is output from the MUX 1103 and acorrection coefficient c(1, 2) that is stored in the LUT, and multipliesthem together. The multiplier 1204 receives the Q signal (pre-correctionQ signal) that is output from the MUX 1103 and a correction coefficientc(2, 2) that is stored in the LUT, and multiplies them together.

The adder 1205 receives outputs of the multipliers 1201 and 1203 andoutputs a corrected I signal (post-correction I signal). The adder 1206receives outputs of the multipliers 1202 and 1204 and outputs acorrected Q signal (post-correction Q signal).

Next, the modulator 1105 will be described.

FIG. 17 is a block diagram showing an example detailed configuration ofthe modulator 1105.

The modulator 1105 includes multipliers 1301 and 1302, an oscillator1303, and an adder 1304.

The multiplier 1301 receives the corrected I signal (post-correction Isignal) that is output from the IQ imbalance corrector 1104 and anoutput of the oscillator 1303, and multiplies them together. Themultiplier 1302 receives the corrected Q signal (post-correction Qsignal) that is output from the IQ imbalance corrector 1104 and anoutput of the oscillator 1303, and multiplies them together.

The oscillator 1303 generates a continuous wave signal, gives a phasedifference of 90° to two continuous wave signals, and supplies theresulting signals to the respective multipliers 1301 and 1302. The adder1304 receives outputs of the multipliers 1301 and 1302 and adds themtogether.

An output of the adder 1304 is a modulated signal, that is, an outputsignal of the transmitter 1100. In the transmitter 1100, an amplifiermay be provided downstream of the modulator 1105. The output signal ofthe transmitter 1100 is given by the following Equation (11) which usesthe amplitude error g_(e) and the phase error θ_(e).

$\begin{matrix}\left\lbrack {{Formula}\mspace{14mu} 11} \right\rbrack & \; \\{V = {{A_{O}\left( {{\left( {1 - g_{e}} \right)I\; ^{j\; \frac{\theta_{c}}{2}}} + {{j\left( {1 + g_{e}} \right)}Q\; ^{{- j}\; \frac{\theta_{e}}{2}}}} \right)}^{j\; \omega \; t}}} & \left( {{Formula}\mspace{14mu} 11} \right)\end{matrix}$

Next, the test signal generator 1101 will be described.

There are two kinds of test signals, that is, a first test signal S10and a second test signal S20. The first test signal S10 is a signal formeasurement of a reference phase of a signal generated by thetransmitter 1100. The second test signal S20 is a signal for measurementof a measurement phase of the signal generated by the transmitter 1100.

First, the first test signal S10 will be described.

For example, the test signal generator 1101 outputs, as the first testsignal S10, a first test signal S11 which is given by the followingEquations (12) and is a signal for determination of a reference phase of0°.

$\begin{matrix}\left\lbrack {{Formulae}\mspace{14mu} 12} \right\rbrack & \; \\\left( \begin{matrix}{I = {A\left( {1 + {\alpha \; {\cos \left( {2\omega_{m}t} \right)}}} \right)}} \\{Q = 0}\end{matrix} \right. & \left( {{Formula}\mspace{14mu} 12} \right)\end{matrix}$

In Equations (12), A and α are constants and ω_(m) is the angularfrequency of a second test signal (single-sideband signal, describedlater). Constant α is determined by the magnitude of IQ imbalance in thetransmitter 1100 and residual IQ imbalance that is permitted after IQimbalance correction. The same applies to Equations to appear below.

In the IQ plane, at t=0 the first test signal S11 which is given byEquations (12) starts oscillating from (I, Q)=(A(1+β), 0) (point A shownin FIG. 18(A)) toward the negative side of the I axis with an amplitudeAα. That is, it is different from a simple test signal that oscillateswith the origin (0, 0) as the center in being offset by a distance A.Therefore, the first test signal S11 that is input to the envelopedetector 1106A can be detected properly if its amplitude A±Aβ fallswithin a detectable range D shown in FIG. 19.

For example, the test signal generator 1101 may output, as the firsttest signal S10, a first test signal S12 that is given by the followingEquations (13), which makes it possible to determine a reference phaseof 90°.

$\begin{matrix}\left\lbrack {{Formulae}\mspace{14mu} 13} \right\rbrack & \; \\\left( \begin{matrix}{I = 0} \\{Q = {A\left( {1 + {\alpha \; {\cos \left( {2\omega_{m}t} \right)}}} \right)}}\end{matrix} \right. & \left( {{Formula}\mspace{14mu} 13} \right)\end{matrix}$

In the IQ plane, at t=0 the first test signal S12 starts oscillatingfrom (I, Q)=(0, A(1+α)) (point B shown in FIG. 18(A)) toward thenegative side of the Q axis with an amplitude Aα. That is, it isdifferent from a simple test signal that oscillates with the origin asthe center in being offset by a distance A in the Q-axis direction.Therefore, the first test signal S12 that is input to the envelopedetector 1106A can be detected properly if its amplitude A±Aα fallswithin the detectable range D shown in FIG. 19.

For example, the test signal generator 1101 outputs, as the first testsignal S10, a first test signal S13 which is given by the followingEquations (14) and is a signal for determination of a reference phase of180°.

$\begin{matrix}\left\lbrack {{Formulae}\mspace{14mu} 14} \right\rbrack & \; \\\left( \begin{matrix}{I = {A\left( {1 - {\alpha \; {\cos \left( {2\omega_{m}t} \right)}}} \right)}} \\{Q = 0}\end{matrix} \right. & \left( {{Formula}\mspace{14mu} 14} \right)\end{matrix}$

In the IQ plane, at t=0 the first test signal S13 which is given byEquations (14) starts oscillating from (I, Q)=(A(1−α), 0) (point A shownin FIG. 18(A)) toward the positive side of the I axis with an amplitudeAα. That is, it is different from a simple test signal that oscillateswith the origin (0, 0) as the center in being offset by a distance A inthe I-axis direction. Therefore, the first test signal S13 that is inputto the envelope detector 1106A can be detected properly if its amplitudeA±Aα falls within the detectable range D shown in FIG. 19.

In Equations (12)-(14), the first test signals S11, S23, and S13 are IQsignals for an amplitude modulation (AM) signal, for example.

Next, the second test signal S20 will be described.

For example, the test signal generator 1101 outputs a second test signalS20 which is given by the following Equations (15):

$\begin{matrix}\left\lbrack {{Formulae}\mspace{14mu} 15} \right\rbrack & \; \\\left( \begin{matrix}{I = {A\; {\cos \left( {\omega_{m}t} \right)}}} \\{Q = {A\; {\sin \left( {\omega_{m}t} \right)}}}\end{matrix} \right. & \left( {{Formula}\mspace{14mu} 15} \right)\end{matrix}$

The second test signal S20 given by the following Equations (15) is anIQ signal for a single-sideband signal which rotates around the origin(0, 0) in the IQ plane. The angular frequency ω_(m) of the second testsignal S20 is half of the angular frequency 2ω_(m) of the first testsignals S11-S13.

Here a description will be made of why the angular frequency ω_(n), ofthe second test signal S20 is set equal to half of the angular frequency2ω_(m) of the first test signals S11-S13.

FIG. 18(A) shows the first test signal S11 and an example ideal secondtest signal S20 in the IQ plane. FIG. 18(B) shows an example second testsignal S20 in which in the IQ plane the I signal is larger than in theideal state and the Q signal is smaller than in the ideal state. Thefirst test signal S11 given by Equations (12) is shown in FIG. 18(A) asan example of the first test signal S10.

In FIG. 18(A), the first test signal S11 vibrates straightly in the IQplane. The second test signal S20 rotates so as to form circles in theIQ plane. For example, in FIG. 18(B), if the second test signal S20 hasdistortion, its amplitude varies in order oflarge→small→large→small→large and the angular frequency varies two timesas it makes one rotation in the IQ plane. Therefore, spurious noiseoccurs at a cycle that is half of the cycle of the second test signalS20.

On the other hand, the amplitude of the first test signal S11 varies inorder of large→small→large and the angular frequency varies once in onecycle. Therefore, when the first test signal 511 is envelope-detected,spurious noise occurs at the same cycle as its cycle.

Therefore, the test signal generator 1101 generates the test signals sothat the angular frequency 2ω_(m) of the first test signal S11 becomestwo times the angular frequency ω_(m) of the second test signal S20.That is, the frequency of the first test signal S10 becomes two timesthat of the second test signal S20.

Next, the envelope detector 1106 will be described.

FIG. 19 shows an example input/output characteristic of the envelopedetector 1106A. The horizontal axis of FIG. 19 represents the magnitudeof the input of the envelope detector 1106A and the vertical axisrepresents the magnitude of the output of the envelope detector 1106A,that is, the input of the AD converter 1106B. It is seen from FIG. 19that the output of the envelope detector 1106A increases steeply in thedetectable range D.

In FIG. 18(A), the first test signal S11 is offset from the origin O topoint A on the I axis in the IQ plane. Therefore, whereas a test signalthat moves on the I axis in the IQ plane so as to pass the origin O doesnot properly fall within the detectable range D, the first test signalS11 falls within the detectable range D properly.

Therefore, all the bits of the AD converter 1106B can be used and hencethe detection accuracy of the envelope detector 1106A is increased. As aresult, a reference phase can be detected accurately.

The test signal generator 1101 adjusts the constant A in each ofEquations (12)-(14) which define the first test signal S10. Morespecifically, the test signal generator 1101 sets the center A (A, 0)(see FIG. 18(A)) of vibration of the first test signal S10 close to thecenter Dm of the detectable range D of the envelope detector 1106Aaccording to the characteristic of the envelope detector 1106A.

Furthermore, the test signal generator 1101 adjusts the constant A inEquations (15) which defines the second test signal S20. Morespecifically, the test signal generator 1101 sets the center ofvibration of the second test signal S20 close to the center Dm of thedetectable range D of the envelope detector 1106A according to thecharacteristic of the envelope detector 1106A. The constant A of thesecond test signal S20 may have the same value as that of the first testsignal S10.

The magnitude of a signal detected by the envelope detector 1106Acorresponds to the absolute value of a resultant vector of the I signaland the Q signal. If the transmitter 1100 does not have IQ imbalance,the magnitude of an envelope of the second test signal S20 detected bythe envelope detector 1106A is constant. On the other hand, if thetransmitter 1100 has IQ imbalance, the magnitude of an envelope of thesecond test signal S20 detected by the envelope detector 1106A varies.

Therefore, whichever of the first test signal S10 and the second testsignal S20 is to be detected, the envelope detector 1106A detects awaveform that vibrates with a point close to the center Dm of thedetectable range D as a vibration center. The first test signal S10 andthe second test signal S20 can also be made approximately the same inamplitude by setting a so that envelope signals of the first test signalS10 and the second test signal S20 are made approximately the same inmagnitude. Therefore, a signal can be detected with high accuracy evenif the dynamic range of the envelope detector 1106A or the AD converter11068 is narrow.

Next, the calculator 1107 will be described.

FIG. 20 is a flowchart showing an example operation of the calculator1107.

The calculator 1107 receives an envelope signal (first envelope)corresponding to the first test signal S10 from the envelope detector1106 (step S101).

Upon receiving the first test signal S10, the calculator 1107 performs afrequency analysis by fast Fourier transform (FFT), for example, andthereby determines a phase θ_(ref) of a component of the angularfrequency ω_(m) (step S102). The phase θ_(ref) serves as a referencephase when the second test signal S20 is used.

The calculator 1107 then receives an envelope signal (second envelope)corresponding to the second test signal S20 from the envelope detector1106 (step S103).

Upon receiving the second test signal S20, the calculator 1107 performsa frequency analysis by fast Fourier transform (FFT), for example, andthereby determines a phase θ_(meas) of a component of the angularfrequency 2ω_(m) (step S104). The phase θ_(meas) is i a measurementphase of the second test signal S20.

Subsequently, the calculator 1107 calculates a phase θ=θ_(meas)−θ_(ref)(step S105). The phase θ is a phase of a component of the angularfrequency 2ω_(m) that is caused by IQ imbalance. The transmitter 1100has a phase rotation of the phase θ_(ref) that is mainly due to delaysin the MUX 1103, the IQ imbalance corrector 1104, the modulator 1105.Therefore, a phase component caused by IQ imbalance can be extracted byeliminating the delay of the system itself using the phase θ.

The calculator 1107 thereafter determines a direction of an amplitudeerror g_(e) or a phase error θ_(e) on the basis of the value of thephase θ (step S106).

FIG. 21 is a table showing an example relationship between the phase θand the IQ imbalance direction. For example, the information of therelationship shown in FIG. 21 is stored in an LUT which is held by thememory 108

As shown in FIG. 21, if −45°≦θ<45°, the calculator 1107 judges that theamplitude error g_(e) is in the negative direction, which means that theI signal component of the output V is larger than in the ideal state. If45°≦θ<135°, the calculator 1107 judges that the phase error θ_(e) is inthe negative direction. If −135°≦θ<180° or −180°≦θ<135°, the calculator1107 judges that the amplitude error g_(e) is in the positive direction.If −135°θ≦−45°, the calculator 1107 judges that the phase error θ_(e) isin the positive direction.

The calculator 1107 then updates the values in the matrix c which isstored in the LUT according to the direction of the amplitude errorg_(e) or the phase error θ_(e) (step S107). The initial values of thevalues in the matrix c are set so as to make it a unit vector. Theaccuracy of the correction coefficients can be increased by updating thematrix c.

For example, if the amplitude error g_(e) is in the negative direction,the calculator 1107 subtracts Δg from the value g_(c) in the elements ofthe matrix c and does not change the value θ_(c). That is, since the Isignal component is larger than in the ideal state if the amplitudeerror g_(e) is in the negative direction, the calculator 1107 updatesthe values in the matrix c so as to decrease the I signal component.

If the phase error θ_(e) is in the negative direction, the calculator1107 subtracts Δθ from the value θ_(c) in the elements of the matrix cand does not change the value g_(c). If the phase error θ_(e) is in thepositive direction, the calculator 1107 adds Δθ to the value θ_(c) inthe elements of the matrix c and does not change the value g_(c). If theamplitude error g_(e) is in the positive direction, the calculator 1107subtracts Δg from the value g_(c) in the elements of the matrix c anddoes not change the value θ_(c).

The parameters Δg and Δθ are adjustment parameters for the amplitudeerror g_(e) and the phase error θ_(e) which are used when IQ calibrationis performed, and are determined by requirements relating to theconvergence time and the convergence accuracy. The IQ imbalancecorrector 1104 performs correction using an updated matrix c.

The calculator 1107 executes the above steps (steps S103-S107) which usethe second test signal S20. The calculator 1107 judges whether or notthe current amplitude of the component of the angular frequency 2ω_(m)is smaller than its preceding amplitude (step S108). If the currentamplitude of the component of the angular frequency 2ω_(m) is smallerthan its preceding amplitude, the process returns to step S103.

Therefore, the amplitude of the component of the angular frequency2ω_(m) becomes smaller and the IQ imbalance of the second test signalS20 is reduced by repeatedly performing a test using the second testsignal.

On the other hand, if the current amplitude of the component of theangular frequency 2ω_(m) is not smaller than its preceding amplitude,the process of FIG. 20 is finished. That is, the calibration is finishedwhen a state that the amplitude of the component of the angularfrequency 2ω_(m) of the second test signal S20 detected by the envelopedetector 1106A no longer becomes smaller is established.

The calculator 1107 calculates a reference phase θ_(ref) for the secondtest signal S20 on the basis of a first envelope corresponding to thefirst test signal S10. The calculator 1107 calculates a measurementphase θ_(meas) on the basis of a second envelope corresponding to thesecond test signal S20. And the calculator 1107 calculates correctioncoefficients on the basis of the measurement phase θ_(meas) and thereference phase θ_(ref). For example, the correction coefficients arethe elements of the matrix c.

More specifically, it is preferable that the calculator 1107 calculate aphase θ by subtracting a reference phase θ_(ref) from a measurementphase θ_(meas) and calculate correction coefficients on the basis of thephase θ. Even more specifically, it is preferable that the calculator1107 estimate the direction of an amplitude error g_(e) or a phase errorθ_(e) contained in IQ imbalance on the basis of the phase θ andcalculate correction coefficients according to of the direction of theamplitude error g_(e) or the phase error θ_(e).

The above operation of the calculator 1107 makes it possible toaccurately estimate a phase θ caused by IQ-imbalance using a referencephase θ_(ref) and hence to increase the accuracy of IQ calibration.

It is preferable that the calculator 1107 calculate a measurement phaseθ_(meas) plural times from the second test signal and calculatecorrection coefficients on the basis of a calculated measurement phaseθ_(meas) and a reference phase plural times. This allows IQ imbalance todecrease gradually and converge.

Next, a description will be made of how the transmitter operates aftercompletion of the calibration.

After completion of the calibration, the transmitter 1100 finishes thecalibration mode. Upon the finish of the calibration mode, thetransmitter 1100 switches to the data transmission mode. Morespecifically, the MUX 1103 shown in FIG. 15 selects the output of thebaseband signal generator 1102.

Then the IQ imbalance corrector 1104 corrects an IQ signal that isoutput from the baseband signal generator 1102 by referring to the LUTin which the correction coefficients calculated by the coefficientscalculator 108 are stored. Subsequently, the modulator 1105 modulates acorrected signal and a modulated signal is transmitted.

The transmitter 1100 can perform IQ imbalance correction with highaccuracy and hence can reduce distortion of a transmission signal evenif the dynamic range of the envelope detector 1106 is narrow. Forexample, IQ calibration may be performed at the time of power-on of thetransmitter 1100 or its reactivation from a sleep mode or before thestart of a data transmission.

Next, a wireless apparatus 1600 including the transmitter 1100 will bedescribed.

FIG. 22 is a block diagram showing an example configuration of thewireless apparatus 1600. The wireless apparatus 1600 is equipped withthe transmitter 1100, a receiver 1602, a duplexer 1603, and an antenna1604.

The transmitter 1100 corrects IQ imbalance, modulates desired data, andtransmits a modulated signal. The receiver 1602 receives data fromanother communication apparatus. The duplexer 1603 separates atransmission signal and a reception signal from each other, whereby theantenna 1604 is shared by transmission and reception.

The wireless apparatus 1600 makes it possible to transmit data havingonly a low degree of distortion.

FIG. 23 shows another wireless apparatus 1700 which is equipped with atransmission antenna 1703 and a reception antenna 1704 which areseparate from each other.

This disclosure is not limited to the configurations of the aboveembodiments. Any configurations are possible as long as they can realizethe functions described in the claims or the functions of theconfigurations of the embodiments.

Although the above embodiments of the disclosure are implemented byhardware, what are described in the disclosure can be implemented bysoftware in cooperation with hardware.

The individual blocks used in describing the embodiments are typicallyimplemented as LSIs which are integrated circuits. They may beimplemented as separate chips or all or part of them may be implementedas one chip. Each such chip may be either called an LSI or called an IC,a system LSI, a super-LSI, or an ultra-LSI depending on its integrationdensity.

The technique for producing an integrated circuit is not limited to thatfor producing an LSI. For example, an FPGA (field programmable gatearray) which can be programmed after manufacture of an LSI or areconfigurable processor in which the connections or settings of circuitcells provided inside an LSI are reconfigurable may be used.

Furthermore, if an integration circuit manufacturing technique thatenables replacement of an LSI is developed because of advancement of thesemiconductor technologies or a rise of a derivative technology, thefunction blocks may naturally be integrated by using that technique. Forexample, the biotechnology is a candidate for such a technology.

(Summary of Modes of Disclosure)

A first transmitter of the disclosure comprises:

a test signal generator configured to generate a test signal;

a frequency characteristics corrector configured to correct an amplitudecharacteristic and a phase characteristic of the test signal generatedby the test signal generator;

a modulator configured to modulate a corrected signal produced by thefrequency characteristics corrector through the correction;

an envelope detector configured to detect an envelope of a modulatedsignal produced by the modulator through the modulation;

a frequency characteristics calculator configured to calculate frequencycharacteristics of an envelope signal detected by the envelope detector;and

a coefficients calculator configured to calculate, on the basis of thefrequency characteristics calculated by the frequency characteristicscalculator, correction coefficients to be used by the frequencycharacteristics corrector to correct the amplitude characteristic andthe phase characteristic of the test signal,

wherein the test signal generator generates a test signal in whichsignal loci in at least two of quadrants of first to fourth quadrants ofthe IQ plane are not symmetrical with each other.

With this configuration, an amplitude characteristic and a phasecharacteristic of a test signal can be acquired by offsetting the testsignal from the origin in the IQ plane. Therefore, correctioncoefficients can be calculated on the basis of the amplitudecharacteristic and the phase characteristic, whereby signal distortioncan be corrected with high accuracy.

A second transmitter of the disclosure is the first transmitter asmodified in such a manner that the test signal generator generates atest signal that rotates along a signal locus line that is offset by aprescribed amount in the IQ plane and is symmetrical with respect to areference axis.

A third transmitter of the disclosure is the first transmitter asmodified in such a manner that the test signal is a signal that rotatesalong a signal locus line at a constant speed.

A fourth transmitter of the disclosure is the second transmitter asmodified in such a manner that the test signal generator generates atest signal that rotates along a circle that is offset by a prescribedamount in the IQ plane.

A fifth transmitter of the disclosure is the fourth transmitter asmodified in such a manner that the test signal is a signal that rotatesat a constant speed along the circle that is offset by the prescribedamount in the IQ plane.

A sixth transmitter of the disclosure is any one of the first to fifthtransmitters as modified in such a manner that:

the test signal generator sweeps the frequency of the test signal in aprescribed frequency range;

the frequency characteristics calculator extracts complex data from anenvelope signal corresponding to each angular frequency component of thetest signal; and

the coefficients calculator calculates each correction coefficient onthe basis of each complex data extracted by the frequencycharacteristics calculator.

A seventh transmitter of the disclosure is the sixth transmitter asmodified in such a manner that the coefficients calculator calculatesreciprocals of the complex data as the correction coefficients,respectively.

An eighth transmitter of the disclosure is the sixth transmitter asmodified in such a manner that the coefficients calculator calculatescorrection coefficients on the basis of a difference between a phasecharacteristic of the complex data and a linear phase characteristic andan amplitude characteristic of the complex data.

A ninth transmitter of the disclosure is any of the sixth to eighthtransmitters as modified in such a manner that it comprises a storageconfigured to store the correction coefficients, and

wherein the coefficients calculator calculates correction coefficientsrepeatedly while updating the correction coefficients stored in thestorage.

A 10th transmitter of the disclosure is the ninth transmitter asmodified in such a manner that the coefficients calculator calculatescoefficients for calculation of the correction coefficients on the basisof the complex data extracted by the frequency characteristicscalculator, and updates the correction coefficients stored in thestorage to a result of adding a weighted version of the coefficientscalculated by the coefficients calculator to the correction coefficientsstored in the storage.

An 11th transmitter of the disclosure is any one of the first to 10thtransmitters as modified in such a manner that the frequencycharacteristics corrector includes:

a converter configured to convert the test signal which is a time-domainsignal into a frequency-domain signal;

a multiplier configured to multiply the frequency-domain signal by thecoefficients calculated by the coefficients calculator; and

an inverse converter configured to convert an output signal of themultiplier which is a frequency-domain signal into a time-domain signal.

A 12th transmitter of the disclosure is any one of the first to 10thtransmitters as modified in such a manner that the frequencycharacteristics calculator includes a converter configured to convertthe envelope signal which is a time-domain signal into afrequency-domain signal.

A 13th transmitter of the disclosure is any one of the first to 10thtransmitters as modified in such a manner that it comprises:

a baseband signal generator configured to generate a baseband signal;and

a transmitter configured to transmit the modulated signal,

wherein the frequency characteristics corrector generates a correctedsignal by correcting the baseband signal on the basis of the correctioncoefficients calculated by the coefficients calculator.

A 14th transmitter of the disclosure comprises:

a test signal generator configured to generate a first test signal and asecond test signal;

a signal corrector configured to correct IQ imbalance of a test signalgenerated by the test signal generator;

a modulator configured to modulate a corrected signal produced by thesignal corrector through the correction;

an envelope detector configured to detect an envelope of a modulatedsignal produced by the modulator through the modulation; and

a correction coefficients processor configured to calculate, on thebasis of the envelope detected by the envelope detector, correctioncoefficients to be used by the signal corrector to correct the IQimbalance,

wherein the test signal generator generates a first test signal and asecond test signal according to a detectable range of the envelopedetector; and

wherein the correction coefficients processor calculates a referencephase of the test signal on the basis of a first envelope correspondingto the first test signal, calculates a measurement phase of the testsignal on the basis of a second envelope corresponding to the secondtest signal, and calculates correction coefficients on the basis of themeasurement phase and the reference phase.

With this configuration, the detection accuracy of the envelope detectoris increased and hence a reference phase can be calculated accurately.Thus, the accuracy of the IQ calibration can be increased.

A 15th transmitter of the disclosure is the 14th transmitter as modifiedin such a manner that the correction coefficients processor calculates aphase of the second test signal by subtracting the reference phase fromthe measurement phase, and calculates correction coefficients on thebasis of the phase.

A 16th transmitter of the disclosure is the 15th transmitter as modifiedin such a manner that the correction coefficients processor estimates adirection of an amplitude error or a phase error contained in the IQimbalance, and calculates correction coefficients according to thedirection of the amplitude error or the phase error.

A 17th transmitter of the disclosure is any one of the 14th to 16thtransmitters as modified in such a manner that:

the first test signal is an IQ signal for an amplitude modulationsignal;

the second test signal is an IQ signal for a single-sideband signal thatrotates in the IQ plane around the origin; and

the first test signal has a frequency that is two times a frequency ofthe second test signal.

An 18th transmitter of the disclosure is any one of the 14th to 17thtransmitters as modified in such a manner that the transmitter comprisesa storage configured to store information of the correctioncoefficients, and

wherein the correction coefficients processor updates the information ofthe correction coefficients stored in the storage to the calculatedcorrection coefficients.

A 19th transmitter of the disclosure is the 18th transmitter as modifiedin such a manner that the correction coefficients processor calculates ameasurement phase of the test signal plural times, and repeatedlycalculates correction coefficients plural times on the basis of thecalculated measurement phase and reference phase.

A 20th transmitter of the disclosure is any one of the 14th to 19thtransmitters as modified in such a manner that transmitter comprises:

a baseband signal generator configured to generate a baseband signal;and

a transmitter configured to transmit the modulated signal,

wherein the signal corrector generates a corrected signal by correctingthe baseband signal on the basis of the correction coefficientscalculated by the correction coefficients processor.

A 21st signal generation device of the disclosure comprises:

a test signal generator configured to generate a test signal;

a frequency characteristics corrector configured to correct an amplitudecharacteristic and a phase characteristic of the test signal generatedby the test signal generator;

a frequency characteristics calculator configured to calculate frequencycharacteristics of an envelope signal of a modulated signal produced bymodulating a corrected signal that is produced by the frequencycharacteristics corrector through the correction; and

a coefficients calculator configured to calculate, on the basis of thefrequency characteristics calculated by the frequency characteristicscalculator, correction coefficients to be used by the frequencycharacteristics corrector to correct the amplitude characteristic andthe phase characteristic of the test signal,

wherein the test signal generator generates a test signal in whichsignal loci in at least two of quadrants of first to fourth quadrants ofthe IQ plane are not symmetrical with each other.

With this configuration, an amplitude characteristic and a phasecharacteristic of a test signal can be acquired by offsetting the testsignal from the origin in the IQ plane. Therefore, correctioncoefficients can be calculated on the basis of the amplitudecharacteristic and the phase characteristic, whereby signal distortioncan be corrected with high accuracy.

A 22nd signal generation device of the disclosure comprises:

a test signal generator configured to generate a first test signal and asecond test signal;

a signal corrector configured to correct IQ imbalance of a test signalgenerated by the test signal generator; and

a correction coefficients processor configured to calculate, on thebasis of an envelope of a modulated signal produced by modulating acorrected signal that is produced by the signal corrector through thecorrection,

wherein the test signal generator generates a first test signal and asecond test signal according to a detectable range of an envelopedetector for detecting the envelope; and

wherein the correction coefficients processor calculates a referencephase of the test signal on the basis of a first envelope correspondingto the first test signal, calculates a measurement phase of the testsignal on the basis of a second envelope corresponding to the secondtest signal, and calculates correction coefficients on the basis of themeasurement phase and the reference phase.

With this configuration, the detection accuracy of the envelope detectoris increased and hence a reference phase can be calculated accurately.Thus, the accuracy of the IQ calibration can be increased.

A 23rd calibration method of the disclosure comprises:

a test signal generation step of generating a test signal;

a frequency characteristics correction step of correcting an amplitudecharacteristic and a phase characteristic of the generated test signal;

a frequency characteristics calculation step of calculating frequencycharacteristics of an envelope signal of a modulated signal produced bymodulating a corrected signal produced through the correction; and

a coefficients calculation step of calculating, on the basis of thecalculated frequency characteristics, correction coefficients to be usedfor correcting the amplitude characteristic and the phase characteristicof the test signal,

wherein the test signal generation step generates a test signal in whichsignal loci in each of at least two pairs of quadrants of first tofourth quadrants of the IQ plane are not symmetrical with each other.

With this method, an amplitude characteristic and a phase characteristicof a test signal can be acquired by offsetting the test signal from theorigin in the IQ plane. Therefore, correction coefficients can becalculated on the basis of the amplitude characteristic and the phasecharacteristic, whereby signal distortion can be corrected with highaccuracy.

A 24th signal generation method of the disclosure comprises:

a test signal generation step of generating a first test signal and asecond test signal;

a correction step of correcting IQ imbalance of a generated test signal;and

a calculation step of calculating, on the basis of an envelope of amodulated signal produced by modulating a corrected signal that isproduced through the correction,

wherein the test signal generation step generates a first test signaland a second test signal according to a detectable range of an envelopedetector for detecting the envelope; and

wherein the calculation step calculates a reference phase of the testsignal on the basis of a first envelope corresponding to the first testsignal, calculates a measurement phase of the test signal on the basisof a second envelope corresponding to the second test signal, andcalculates correction coefficients on the basis of the measurement phaseand the reference phase.

With this method, the detection accuracy of the envelope detector isincreased and hence a reference phase can be calculated accurately.Thus, the accuracy of the IQ calibration can be increased.

Although the disclosure has been described in detail with reference tothe particular embodiments, it is apparent that those skilled in the artcould make various changes or modifications without departing from thespirit and scope of the disclosure.

The present application is based on Japanese Patent Application No.2012-074719 filed on Mar. 28, 2012 and Japanese Patent Application No.2012-078308 filed on Mar. 29, 2012, the disclosures of which areincorporated herein by reference.

INDUSTRIAL APPLICABILITY

For example, this disclosure is useful when applied to transmitters,signal generation devices, calibration methods, etc. which can correctsignal distortion with high accuracy. For example, this disclosure isalso useful when applied to transmitters, signal generation devices,calibration methods, etc. which can increase the accuracy of IQcalibration.

DESCRIPTION OF SYMBOLS

-   100: Transmitter-   101: Test signal generator-   102: Data generator-   103: MUX-   104: Frequency characteristics corrector-   105: Modulator-   106: Envelope detector-   106A: Envelope detector-   106B: AD converter-   107: Frequency characteristics calculator-   108: Coefficients calculator-   109: Memory-   204: Fourier transformer-   205: Multiplier-   206: Inverse Fourier transformer-   301: Digital filter-   400: Wireless apparatus-   402: Receiver-   403: Duplexer-   404: Antenna-   500: Wireless apparatus-   502: Receiver-   503, 504: Antenna-   1100: Transmitter-   1101: Test signal generator-   1102: Baseband signal generator-   1103: MUX-   1104: IQ imbalance corrector-   1105: Modulator-   1106: Envelope detector-   1106A: Envelope detector-   1106B: AD converter-   1107: calculator-   1108: Memory-   1201, 1202, 1203, 1204: Multiplier-   1205, 1206: Adder-   1301, 1302: Multiplier-   1303: Oscillator-   1304: Adder-   1600: Wireless apparatus-   1602: Receiver-   1603: Duplexer-   1604: Antenna-   1700: Wireless apparatus-   1702: Receiver-   1703, 1704: Antenna

1. A transmitter comprising: a test signal generator configured togenerate a test signal; a frequency characteristics corrector configuredto correct an amplitude characteristic and a phase characteristic of thetest signal generated by the test signal generator; a modulatorconfigured to modulate a corrected signal produced by the frequencycharacteristics corrector through the correction; an envelope detectorconfigured to detect an envelope of a modulated signal produced by themodulator through the modulation; a frequency characteristics calculatorconfigured to calculate frequency characteristics of an envelope signaldetected by the envelope detector; and a coefficients calculatorconfigured to calculate, on the basis of the frequency characteristicscalculated by the frequency characteristics calculator, correctioncoefficients to be used by the frequency characteristics corrector tocorrect the amplitude characteristic and the phase characteristic of thetest signal, wherein the test signal generator generates a test signalin which signal loci in at least two of quadrants of first to fourthquadrants of the IQ plane are not symmetrical with each other.
 2. Thetransmitter according to claim 1, wherein the test signal generatorgenerates a test signal that rotates along a signal locus line that isoffset by a prescribed amount in the IQ plane and is symmetrical withrespect to a reference axis.
 3. The transmitter according to claim 1,wherein the test signal is a signal that rotates along a signal locusline at a constant speed.
 4. The transmitter according to claim 2,wherein the test signal generator generates a test signal that rotatesalong a circle that is offset by a prescribed amount in the IQ plane. 5.The transmitter according to claim 4, wherein the test signal is asignal that rotates at a constant speed along the circle that is offsetby the prescribed amount in the IQ plane.
 6. The transmitter accordingto claim 1, wherein the test signal generator sweeps the frequency ofthe test signal in a prescribed frequency range; wherein the frequencycharacteristics calculator extracts complex data from an envelope signalcorresponding to each angular frequency component of the test signal;and wherein the coefficients calculator calculates each correctioncoefficient on the basis of each complex data extracted by the frequencycharacteristics calculator.
 7. The transmitter according to claim 6,wherein the coefficients calculator calculates reciprocals of thecomplex data as the correction coefficients, respectively.
 8. Thetransmitter according to claim 6, wherein the coefficients calculatorcalculates correction coefficients on the basis of an amplitudecharacteristic of the complex data and a difference between a phasecharacteristic of the complex data and a linear phase characteristic. 9.The transmitter according to claim 6, further comprising: a storageconfigured to store the correction coefficients, wherein thecoefficients calculator calculates correction coefficients repeatedlywhile updating the correction coefficients stored in the storage. 10.The transmitter according to claim 9, wherein the coefficientscalculator calculates coefficients for calculation of the correctioncoefficients on the basis of the complex data extracted by the frequencycharacteristics calculator, and updates the correction coefficientsstored in the storage to a result of adding a weighted version of thecoefficients calculated by the coefficients calculator to the correctioncoefficients stored in the storage.
 11. The transmitter according toclaim 1, wherein the frequency characteristics corrector includes: aconverter configured to convert the test signal which is a time-domainsignal into a frequency-domain signal; a multiplier configured tomultiply the frequency-domain signal by the coefficients calculated bythe coefficients calculator; and an inverse converter configured toconvert an output signal of the multiplier which is a frequency-domainsignal into a time-domain signal.
 12. The transmitter according to claim1, wherein the frequency characteristics calculator includes a converterconfigured to convert the envelope signal which is a time-domain signalinto a frequency-domain signal.
 13. The transmitter according to claim1, further comprising: a baseband signal generator configured togenerate a baseband signal; and a transmitter configured to transmit themodulated signal, wherein the frequency characteristics correctorgenerates a corrected signal by correcting the baseband signal on thebasis of the correction coefficients calculated by the coefficientscalculator.
 14. A transmitter comprising: a test signal generatorconfigured to generate a first test signal and a second test signal; asignal corrector configured to correct IQ imbalance of a test signalgenerated by the test signal generator; a modulator configured tomodulate a corrected signal produced by the signal corrector through thecorrection; an envelope detector configured to detect an envelope of amodulated signal produced by the modulator through the modulation; and acorrection coefficients processor configured to calculate, on the basisof the envelope detected by the envelope detector, correctioncoefficients to be used by the signal corrector to correct the IQimbalance, wherein the test signal generator generates a first testsignal and a second test signal according to a detectable range of theenvelope detector; and wherein the correction coefficients processorcalculates a reference phase of the test signal on the basis of a firstenvelope corresponding to the first test signal, calculates ameasurement phase of the test signal on the basis of a second envelopecorresponding to the second test signal, and calculates correctioncoefficients on the basis of the measurement phase and the referencephase.
 15. The transmitter according to claim 14, wherein the correctioncoefficients processor calculates a phase of the second test signal bysubtracting the reference phase from the measurement phase, andcalculates correction coefficients on the basis of the phase.
 16. Thetransmitter according to claim 15, wherein the correction coefficientsprocessor estimates a direction of an amplitude error or a phase errorcontained in the IQ imbalance, and calculates correction coefficientsaccording to the direction of the amplitude error or the phase error.17. The transmitter according to claim 14, wherein the first test signalis an IQ signal for an amplitude modulation signal; wherein the secondtest signal is an IQ signal for a single-sideband signal that rotates inthe IQ plane around the origin; and wherein the first test signal has afrequency that is two times a frequency of the second test signal. 18.The transmitter according to claim 14, further comprising: a storageconfigured to store information of the correction coefficients, whereinthe correction coefficients processor updates the information of thecorrection coefficients stored in the storage to the calculatedcorrection coefficients.
 19. The transmitter according to any one ofclaim 18, wherein the correction coefficients processor calculates ameasurement phase of the test signal plural times, and repeatedlycalculates correction coefficients plural times on the basis of thecalculated measurement phase and reference phase.
 20. The transmitteraccording to claim 14, further comprising: a baseband signal generatorconfigured to generate a baseband signal; and a transmitter configuredto transmit the modulated signal, wherein the signal corrector generatesa corrected signal by correcting the baseband signal on the basis of thecorrection coefficients calculated by the correction coefficientsprocessor.
 21. A signal generation device comprising: a test signalgenerator configured to generate a test signal; a frequencycharacteristics corrector configured to correct an amplitudecharacteristic and a phase characteristic of the test signal generatedby the test signal generator; a frequency characteristics calculatorconfigured to calculate frequency characteristics of an envelope signalof a modulated signal produced by modulating a corrected signal that isproduced by the frequency characteristics corrector through thecorrection; and a coefficients calculator configured to calculate, onthe basis of the frequency characteristics calculated by the frequencycharacteristics calculator, correction coefficients to be used by thefrequency characteristics corrector to correct the amplitudecharacteristic and the phase characteristic of the test signal, whereinthe test signal generator generates a test signal in which signal lociin at least two of quadrants of first to fourth quadrants of the IQplane are not symmetrical with each other.
 22. A signal generationdevice comprising: a test signal generator configured to generate afirst test signal and a second test signal; a signal correctorconfigured to correct IQ imbalance of a test signal generated by thetest signal generator; and a correction coefficients processorconfigured to calculate, on the basis of an envelope of a modulatedsignal produced by modulating a corrected signal that is produced by thesignal corrector through the correction, wherein the test signalgenerator generates a first test signal and a second test signalaccording to a detectable range of an envelope detector for detectingthe envelope; and wherein the correction coefficients processorcalculates a reference phase of the test signal on the basis of a firstenvelope corresponding to the first test signal, calculates ameasurement phase of the test signal on the basis of a second envelopecorresponding to the second test signal, and calculates correctioncoefficients on the basis of the measurement phase and the referencephase.
 23. A calibration method comprising: a test signal generationstep of generating a test signal; a frequency characteristics correctionstep of correcting an amplitude characteristic and a phasecharacteristic of the generated test signal; a frequency characteristicscalculation step of calculating frequency characteristics of an envelopesignal of a modulated signal produced by modulating a corrected signalproduced through the correction; and a coefficients calculation step ofcalculating, on the basis of the calculated frequency characteristics,correction coefficients to be used for correcting the amplitudecharacteristic and the phase characteristic of the test signal, whereinthe test signal generation step generates a test signal in which signalloci in each of at least two pairs of quadrants of first to fourthquadrants of the IQ plane are not symmetrical with each other.
 24. Asignal generation method comprising: a test signal generation step ofgenerating a first test signal and a second test signal; a correctionstep of correcting IQ imbalance of a generated test signal; and acalculation step of calculating, on the basis of an envelope of amodulated signal produced by modulating a corrected signal that isproduced through the correction, wherein the test signal generation stepgenerates a first test signal and a second test signal according to adetectable range of an envelope detector for detecting the envelope; andwherein the calculation step calculates a reference phase of the testsignal on the basis of a first envelope corresponding to the first testsignal, calculates a measurement phase of the test signal on the basisof a second envelope corresponding to the second test signal, andcalculates correction coefficients on the basis of the measurement phaseand the reference phase.